"The overriding challenge for our generation is to build a new economy–one that is powered largely by renewable sources of energy, that has a much more diversified transport system, and that reuses and recycles everything." –Lester R. Brown, Plan B 3.0: Mobilizing to Save Civilization

Chapter 8. Raising Land Productivity: Multiple Cropping

In North America and Western Europe, which in the past have restricted cropped area in order to avoid surpluses, there is a potential for double cropping that has not been fully exploited. Indeed, the tripling in the world grain harvest since 1950 is due in part to impressive increases in multiple cropping in Asia. As noted in Chapter 3, some of the more common multiple cropping combinations are wheat and corn in northern China, wheat and rice in northern India, and the double or triple cropping of rice in southern China and southern India.12

The double cropping of winter wheat and corn in the North China Plain helped make China the world's leading grain producer. Winter wheat grown there yields close to 4 tons per hectare. Corn averages 5 tons. Together these two crops, grown in rotation, can yield 9 tons of grain per hectare per year. Double cropping of rice yields 8 tons per hectare.13

A generation ago in India, land in the north was devoted to producing only wheat, but with the advent of earlier maturing, high-yielding wheats and rices, it became possible to harvest the wheat in time to plant rice. This wheat/rice combination is now widely used throughout Punjab, Haryana, and parts of Uttar Pradesh. The rice yield of 2 tons per hectare and the wheat yield of 3 tons combine for 5 tons of grain per hectare, making it a key to feeding India's 1 billion people.14

The area that can be multiple cropped is limited by the availability of irrigation water, early-maturing varieties, and, in developing countries, enough labor to quickly harvest one crop and plant another. The loss of low-cost rural laborers through the processes of industrialization can sharply reduce multiple cropping and therefore the harvested area. In Japan, for example, the grain-harvested area in 1961 reached a peak of nearly 5 million hectares, because farmers were harvesting an average of two crops per year. As of 2002, the harvested area had dropped to 2 million hectares, partly because of cropland conversion to nonfarm uses, but mostly because of a dramatic decline in double cropping as industry pulled labor from agriculture. Even a rice-support price four times the world market price could not keep enough workers in agriculture to support extensive multiple cropping.15

South Korea's harvested area has shrunk by half since peaking in 1965. Taiwan's has declined nearly two thirds since 1975. As industrialization progresses in China and India, the more prosperous regions of these countries may see similar declines in multiple cropping. In China, where incomes have quadrupled since 1980, this process already appears to be reducing production.16

In the United States, the lifting of planting area restrictions in 1996 opened new opportunities for multiple cropping. The most common U.S. double cropping combination is winter wheat with soybeans as a summer crop. Six percent of the soybean harvest comes from land that also produces winter wheat. One benefit of this rotation is that soybeans fix nitrogen, reducing the amount of fertilizer needed for wheat.17

A concerted U.S. effort to both breed earlier maturing varieties and develop cultural practices that would facilitate multiple cropping could substantially boost crop output. If China's farmers can extensively double crop wheat and corn, then U.S. farmers, at a similar latitude and with similar climate patterns, might be able to do the same if agricultural research and farm policy were reoriented in support of such an initiative.

Western Europe, with its mild winters and high-yielding wheat, might also be able to double crop more with a summer grain, such as corn, or with an oilseed crop. Elsewhere in the world, Brazil and Argentina have an extended frost-free growing season climate that supports extensive multiple cropping, often wheat or corn with soybeans.18